Increase power of emitters on objects?
The closest thing I can think of is doubling the entire shader of the object you want to be more illuminated.  This is done by adding the shader to itself.  To do this plug plug your shader nodes into both sockets of an add shader at the very end of the node tree.



It produces the following result.  The center ball uses the above technique while the other two use just the node group.



The disadvantage of this is that it doubles all rays hitting the object, not just ones from a specific emitter.

See this post and this post for more on the add shader node.